The properties and capabilities are described of a biosensor instrument that will be used to define interactions between macromolecules. Its acquisition would establish one of an array of instruments to be used for this purpose. The proposal is submitted by seven investigators involved in studies on protein-protein, ligand-protein, peptide-protein, or protein-membrane interactions, who have expertise in high resolution protein structure studies, and in areas of biochemistry, biophysics, and molecular genetics. The biosensor instrumentation would complement and extend the information obtained from the high resolution structure studies by providing information on protein function and mechanism. A wide range of problems will be addressed. These include: (i) the nature of the membrane binding affinity of "membrane-active" proteins; (ii) the interaction between colicins and their cellular receptor; (iii) the binding affinity of antibodies to human rhinovirus; (iv) receptor interactions of enterotoxins; (v) altered binding of NAD+ by Asian alcohol dehydrogenase; (vi) binding of mitochondrial leader peptides to their receptors; (vii) interaction of G protein receptors with caveolin; (viii) interactions of erythrocyte band III peptide with glycolytic enzymes, and of lyn tyrosine kinase and B-cell antigen receptor; (ix) SH2-mediated interactions between p72 syk and the src-family kinase lck; (x) profilin-actin interactions and their modulation by ligands including proline-rich proteins and phosphoinositide lipids.